Research Reports

An Analysis of the Puget Sound In-Vehicle Traffic Map Demonstration

Description:

The purposes of this project were to gain a better understanding of the benefits of providing in-vehicle congestion information and to determine whether any detectable congestion level changes resulted from providing this information. The project tested an in-vehicle traffic map device (TrafficGauge) using 2,215 participants from the Puget Sound region. Three rounds of surveys (Entry, Daily and Exit) took place between November 2007 and May 2008 in which participants used the TrafficGauge for six months. The project also analyzed a roadway corridor to determine, in instances of unusual freeway congestion, how traveler’s behavior affects congestion on alternative roadways. The analysis looked for correlations between the performance of the study corridor’s three freeways and four arterials using conditional probability tables.

Most of the survey participants were young to middle-age males, well educated with middle or high incomes. The entry survey demographic data indicated that the participants were not representative of the general population but they were probably representative of those most likely to seek and pay for traveler information, particularly information delivered by an in-vehicle congestion map device.

On half the occasions when participants reported changing routines in the daily surveys, they reported not receiving any benefits. For the entire study, 25 percent of participants reported not benefiting at all from the device. Participants who changed routines saved time a mean number of 1.6 times. The mean amount of time saved on those instances was a little over 30 minutes. Thirty-two percent of participants indicated that they did not save any time by using the device. Over 59 percent of the participants indicated that the information provided by the device reduced their level of stress.

The study participants could be divided into three groups. One (about 20 percent) thought highly of the device, were confident that it had saved them considerable time and stress, and would purchase the device. Another (between 21 percent and 26 percent) saw little value in either the device or the information that it conveyed and would not purchase the device. The third, and largest, group saw value in the device and occasionally benefited from the information it provided. They did not, however, think that these benefits warranted purchasing the device.

The corridor analysis indicated that even without arterial performance information, some travelers seek alternative routes when the freeway becomes congested. The corridor analysis confirmed that many travelers diverted either on the basis of what they see on the roadway or what they get from en-route traffic information sources. Even the modest levels of diversion observed in this study increased arterial congestion, especially near freeway ramps. This visible arterial congestion near the freeway discouraged diversion. Consequently, providing arterial performance information on the entire arterial via in-vehicle devices is likely to increase initial diversion, thereby degrading arterial performance. Roadway agencies will, therefore, need to make traffic management of the ramps and arterial segments that connect the alternate routes a priority.